Washing machine smells bad

Noticed on the last two loads of laundry that the clothing didn't smell all that great coming out of the washer, and there is a fairly pungent smell in the drum after washing. It smells like I forgot to put soap in or something, but I know I didn't. The laundry wasn't preticularly dirty so I'm not sure what is causing this. Anyone have any ideas what might cuase this to happen? It is a Bosch front loader, about 3/4 years old. Thanks for any ideas.